As with iTunes (which is only slated to arrive sometime this year), the Spotify launch is really about ensuring that Windows 10 S users have access to must-have software that hasn't been available in the Windows Store until now. You're theoretically less likely to jump ship for Google's Chrome OS if you know that you can get a comparable Windows 10 S PC with native desktop apps, not just web or Android apps. While there's no guarantee Microsoft will succeed with this strategy, it was certainly going to face an uphill battle without Spotify's support.